Conditioned sodium chloride



CONDITIONED SODIUM CHLORIDE Russell N. Bell, Clarendon Hills, and LowellE. Netherton, Park Forest, 111., 'assignors to Victor Chemical Works, acorporation of Illinois No Drawing. Original application August 20,1954, Se-

nal No. 451,302, now Patent No. 2,852,341, dated September 16, 1958.Divided and this application February 19, 1958, Serial No. 716,025

2 Claims. (Cl. 23-89) States Patent Patented Jan. 26, 1960 thuscorresponds to a range of analytical ratios from having a ratio of CaO/PO from 1.66 to 2 moles of the calcium oxide to each mole of the P 0 inwhich the water of hydration is markedly less than the product found bySchwarz, which has a very low bulk density, and submicroscopic crystalsize.

Strangely enough, very slight deviations in the method of preparing thematerial markedly change the crystal size and the bulk density, andthese changes markedly and adversely afiect the properties of thecalcium phosphate.

The preferred material has approximately 8 molecules of water ofhydration (compared to roughly molecules of water of hydration in theSchwarz product). The present product may be dehydrated either to atetrahydrate or to the anhydrous product without impairing its desirableproperties.

The preferred product has a bulk density as low as 5 pounds per cubicfoot. Its crystal size is submicroscopic and apparently well below 1micron. A mass of the product will move under local pressure much like aliquid.

The product of this invention is remarkable in its conditioning andstabilizing qualities when mixed with various other salts. For example,small quantities of the calcium polyphosphate, when added to normalyhygroscopic table salt (i.e., sodium chloride) render it more resistantto moisture than other commonly used conditioners. It is also extremelyvaluable as a stabilizer when added to unstable hydrated salts such asdicalcium phosphate dihydrate.

The new product may be made by adding a 5-15% solution of sodiumtripolyphosphate to a 2-l0% solution of calcium chloride with constantagitation at a temperature of from approximately 50 to 100 C. Theresulting slurry is then rapidly adjusted to a pH of approximately 9with a small amount of lime and filtered immediately. It may be washedwith hot water to reduce the residual chlorides and is then dried.

The reaction conditions are extremely critical. Thus if moreconcentrated solutions of the reactants are used, a mixed sodium calciumtripolyphosphate is formed. =If lower temperatures are used, the productis composed of larger, more dense crystals which do not possess theunique stabilizing and conditioning ability. If the crystals are notfiltered immediately, the stabilizing ability is lost. If even the orderof addition is reversed, the resulting product does not possess thisstabilizing ability.

The preferred form of this new product appears to be primarily calciumtripolyphosphate octahydrate The composition does not appear to be thecritical factor, however, as products with ratios varying fromapproximately 1.66 to 2.00 have possessed satisfactory conditioning andstabilizing action when prepared according to the present invention. Incontrast, material with an analysis and ratio exactly corresponding tothe above formula, but prepared by a difierent method, does not possessthis stabilizing action. Likewise material which corresponded to anoctahydrate when dried at room temperature retained an excellentstabilizing action upon being successively dehydrated to thetetrahydrate at approximately 110 C. and to the anhydrous salt atapproximately 420 C. Only at temperatures near 450 C. did thisstabilizing action disappear.

The calcium chloride suitable for this process is the ordinarycommercial product. It should be understood that any other solublecalcium salt may be used as a source of calcium ions, but that calciumchloride is the most economically feasible compound.

The sodium tripolyphosphate suitable for use is the ordinary commercialproduct and should analyze at least 90% sodium tripolyphosphate. Othersources of the triphosphate ion such as potassium tripolyphosphate willalso produce the desired product, but are again impractical from aneconomic standpoint.

The following examples illustrate the preparation of theproduct:

EXAMPLE I 194 g. of sodium tripolyphosphate were dissolved in 2000 ml.water (9.7% soln.) and added to 153 g. calcium chloride dissolved in3500 ml. water (4.7% soln. and 5% excess over sodium tripolyphosphate)at to C. The addition took one hour after which the solution wasneutralized to a pH of 7-8 by adding 7-8 g. of dry hydrated lime andimmediately filtered. The resulting filter cake waswashed with 2000 ml.Water at room temperature. The cake was then air dried at roomtemperature. The product analyzed as follows: Ca0=33.8%, P 0 =46.2%,ratio CaO/P O =.73, loss on ignition=19.l%. The pH of a 1% solution ofthe product was 7.0.

EXAMPLE II In a similar manner, 37 g. of sodium tripolyphosphate weredissolved in 400 ml. Water (8.5% soln.) and rapidly added to a solutionof 28 g. CaCl in 700 ml. of Water (3.8% soln.) at 75 to C. with vigorousagitation. The resulting crystals were filtered, washed withapproximately a liter of cold Water, and dried at C.

Analysis.-Ca0=35.l%, P O =53.2%, ratio=0.66,.

loss=9.7%.

EXAMPLE III A series of similar charges were made in which a hot,.

a hot, dilute solution of calcium chloride with vigorous agitation. ThepH was adjusted by adding calcium hydroxide. The following table of datasets forth the pertinent information obtained, I

All of these products were found to possess excellent stabilizing andconditioning qualities. The products were extremely light weight, arepresentative sample having a bulk density of only 5 lb./ft.

EXAMPLE IV In a similar manner a 9.1% solution of potassiumtripolyphosphate was added to a 5% solution of calcium chloride at 7075C. The product had good stabilizing characteristics.

X-ray tests on all of these products showed crystalline characteristicsof a single compound. The diiferences in the ratio of calcium oxide to Pis not thoroughly understood since the X-ray indicates the presence ofone dominant compound in all cases. It may be that the deviationsrepresent the presence of some unreacted calcium oxide as an impurity.

The critical nature of the order of addition is indicated by thefollowing tests:

EXAMPLE V A 15% solution of calcium chloride was added to a 4.5%solution of sodium tripolyphosphate with constant agitation at 80 C. Theproduct had a. CaO/P O ratio of 0.62, but the product was of acomparatively coarse dense nature. Similar attempts at reversing theorder of addition using various concentrations of solutions running from4.0 to 15.0% for the calcium chloride, and from 4.5 to 13.6% for thetripolyphosphate failed to produce a satisfactory product. The materialwas always of a more dense nature and did not possess stabilizing andconditioning characteristics. A representative sample of this materialhad a bulk density of 18.71bs./ft.

The excellent conditioning action of the compound of the presentinvention may be illustrated by its action when mixed with common tablesalt. It is well known that such salt is somewhat hygroscopic and easilycaked in its normal state. One means for evaluating its resistance tomoisture is to slowly drop water into a known quantity of salt until itwill no longer freely ilow through a glass laboratory funnel. Thefollowing test shows a comparison between calcium polyphosphate preparedas in Example III and tricalcium phosphate which is well known for itsability to render salt resistant to moisture.

EXAMPLE VI Two IOO-gram portions of untreated common table salt whichhad been thoroughly dried were mixed with Z-grarn portions of calciumpolyphosphate and tricalcium phosphate, respectively. Water was thenadded dropwise until each mixture caked sufiiciently to prevent itsflowing through a glass funnel. The sample which was conditioned withcalcium polyphosphate absorbed 44 drops of water. The sample conditionedwith an equivalent amount of the customary tricalcium phosphate absorbedonly 23 drops which indicates that it is only about one half aseffective as a salt conditioner.

A test of the ability of this new material to exert a stabilizing actionon other finely divided materials is demonstrated with dicalciumphosphate dihydrate. This material is well known as being verysusceptible to damage from caking due to dehydration. Dicalciumphosphate dihydrate will lose water and convert to the anhydrous formeven'when stored at a relative humidity of 75% at a temperature of 60 C.It is during this change in the degree of hydration that caking occurs.Therefore, the resulting degree of hydration expressed in terms ofpercent anhydrous material serves as a convenient index for comparingthe stability to caking of different lots of material.

It has been found that addition of calcium polyphosphate to dicalciumphosphate dihydrate, either during manufacture or by simply mixing withthe finished product, greatly increases the stability of this compound.The following data compare untreated dicalcium phosphate dihydrate withvariously treated material after storage for .48 hours at 60* VC. and75% relative humidity.

EXAMPLE VII Percent decom- Semple posed to anhydrous form 97.5%decomposed. 37% decomposed.

Regular material 1% calcium polyphosphate added after mfg 29 calciumpolyphosphate added after mfg 22% decomposed. 3% calc um polyphosphateadded after mfg. 15.5 o decomposed. 4% calcium polyphosphate added aftermfg. 6.5% decomposed. 25% calcium polyphosphate added during mfg... 3.0%decomposed.

Percent 0-2.5 microns diameter 6.0 2.5-5 microns diameter 83.1 5-10microns diameter 6.8 10-20 microns diameter 4.0 20 microns diameter NilThis application is a division of our allowed, copending applicationentitled Calcium Polyphosphate and Methodv of Producing the Same, SerialNo. 451,302, filed August 20, 1954, which issued as Patent 2,852,341.

The foregoing detailed description has been given for clearness ofunderstanding only and no unnecessary limitations should be understoodtherefrom as modifications will be obvious to those skilled in the art.

We claim:

1. Conditioned sodium chloride having free-flowing, non-cakingproperties, which comprises sodium chloride and a minor proportion of awater-insoluble calcium polyphosphate having submicroscopic crystals ofless than one micron size and the property of conditioning sodiumchloride, said calcium polyphosphate produced by the process whichcomprises adding a 5 to 15% solution of an alkali metal tripolyphosphateto a 2 to 10% solution of a soluble calcium salt at a temperaturebetween 50 and C., rapidly adjusting the pH of the resulting slurry toapproximately 7-10, immediately removing the resulting crystals ofcalcium polyphosphate from the reaction mixture, and drying the same.

2. Conditioned sodium chloride having free-flowing, non-cakingproperties, which comprises sodium chloride and about 0.1% to about 5%of a water-insoluble calcium polyphosphate having submicroscopiccrystals of less than one micron size and the property of conditioningsodium chloride, said calcium polyphosphate produced by the processwhich comprises adding a 5 to 15% solution of an alkali metaltripolyphosphate to a 2 to 10% solution of a soluble calcium salt at atemperature between 50 and 100 C., rapidly adjusting the pH of theresulting slurry to approximately 7-10, immediately removing theresulting crystals of calcium polyphosphate from the reaction mixture,and drying the same.

References Cited in t he file of this patent UNITED STATES PATENTS Re.18,907 Warning et a1 Aug. 1, 1933 352,465 Hughes Nov. 9, 1886 OTHERREFERENCES Moss et al.: Tricalcium Phosphate as a Caking Inhibitor,"published in Industrial and Engineering Chemistry, vol. 25, No. 2(February 1933), pp 142-146.

1. CONDITIONED SODIUM CHLORIDE HAVING FREE-FLOWING, NON-CAKINGPROPERTIES, WHICH COMPRISES SODIUM CHLORIDE AND A MINOR PROPORTION OF AWATER-INSOLUBLE CALCIUM POLYPHOSPHATE HAVING SUBMICROSCOPIC CRYSTALS OFLESS THAN ONE MICRON SIZE AND THE PROPERTY OF CONDITIONING SODIUMCHLORIDE, SAID CALCIUM POLYPHOSPHATE PRODUCED BY THE PROCESS WHICHCOMPRISES ADDING A 5 TO 15% SOLUTION OF AN ALKALI METAL TRIPOLYPHOSPHATETO A 2 TO 10% SOLUTION OF A SOLUBLE CALCIUM SALT AT A TEMPERATUREBETWEEN 50* AND 100*C., RAPIDLY ADJUSTING THE PH OF THE RESULTING SLURRYTO APPROXIMATELY 7-10, IMMEDIATELY REMOVING THE RESULTING CRYSTALS OFCALCIUM POLYPHOSPHATE FROM THE REACTION MIXTURE, AND DRYING THE SAME.